In Pursuit Of The Perfect Injection Moulded Part 4 – Vacuum Voids

PublishedJanuary 1, 2018

It is very easy to make expensive errors when it comes to injection moulding. Quality issues in injection-moulded products can range from minor surface defects to more serious problems that can affect the safety, performance and function of the product. They can be caused by problems related to the moulding process, material use, toolingdesign or a combination of all three.

This is the fourth on our series of posts where we look at a number of issues that can affect the quality of the end product and some of the common remedies. This post is about vacuum voids.

Vacuum voids / air pockets

Vacuum voids, or air pockets, are trapped air bubbles that appear in a finished moulded component. Quality control professionals typically consider voids to be a ‘minor’ defect. But larger or more numerous voids can weaken the moulded part in some cases, as there’s air below the surface of the part where there should be moulded material.

Common causes of and steps to prevent vacuum voids in moulded parts

One of the chief causes of voids is inadequate moulding pressure to force trapped air out of the mould cavity. Other times, the material closest to the mould wall cools too quickly, causing the material to harden and pull the material toward the outside, creating an abscess. The material itself may be especially vulnerable to voids if its density changes significantly from the molten to hardened state. Voids are more difficult to avoid in moulded parts which are thicker than 6 mm. Common ways to prevent voids include:

Raise the injection pressure to force out trapped air pockets

Choose a grade of material with lower viscosity to limit the risk of air bubbles forming

Place gates close to the thickest parts of the mould to prevent premature cooling where the material is most vulnerable to voids.

Patterson & Rothwell are a Plastic Injection Moulding Company based in the North West of England, UK producing goods for many business sectors. Our ethos is to offer our customers a professional yet flexible approach and of course provide attention to detail at every stage. Please contact us if you wish to discuss any Plastic Injection Moulding Project.

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